Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.36   7.240%   $255.6173   $255.62   $255.60   $255.60  
  Purchase #2 $130.32   10.784%   $144.3737   $144.37   $144.35   $144.40  
  Purchase #3 $122.90   4.311%   $128.1982   $128.20   $128.20   $128.20  
  Purchase #4 $76.59   11.316%   $85.2569   $85.26   $85.25   $85.30  
  Purchase #5 $181.63   12.674%   $204.6498   $204.65   $204.65   $204.60  
  Purchase #6 $71.77   5.406%   $75.6499   $75.65   $75.65   $75.60  
  Purchase #7 $43.79   6.153%   $46.4844   $46.48   $46.50   $46.50  
  7 purchase totals = $865.36       $940.2302   $940.23   $940.20   $940.20